In treating a dental viscous material with a high viscosity such as a dental filling material, an artificial tooth material, and a tooth crown material in the dental field, a viscous material container such as a dental viscous material container that is a disposable container filled with the dental viscous material is used. The dental viscous material container is set onto a dedicated pushing device with a handle, and the handle of the pushing device is operated to discharge an appropriate amount of the dental viscous material from the dental viscous material container.
JP10-179608A describes an example of the viscous material container according to the related art. The viscous material container includes a housing including a first section, a second section, and a third section. The first section has an insertion port at an end thereof, and includes a first inner wall surface configured to surround a first passage extending along an imaginary center line from the insertion port and having a transverse sectional shape that is circular about the imaginary center line. The second section has a discharge port at an end thereof, and includes a second inner wall surface configured to surround a second passage extending from the discharge port. The third section is positioned between the first section and the second section, and includes a third inner wall surface configured to surround a third passage communicating with the first passage and the second passage. A piston is inserted into the first passage to push out a viscous material, which is contained in the first passage, from the discharge port through the second and third passages. As illustrated in FIG. 1 of JP10-179608A, the piston (13) includes: one seal ring (14) configured to contact the first inner wall surface as the piston is inserted in the first passage; and a pair of non-contact portions (15) configured not to contact the first inner wall surface as the piston is inserted in the first passage, located at both sides of the seal ring (14) in the direction of extension of the imaginary center line and having an outside diameter that is smaller than that of the seal ring (14). The pair of non-contact portions (15) of the piston (13) is shaped to be plane-symmetric with respect to an imaginary surface that includes the seal ring (14) and is orthogonal to the imaginary center line.